Two days after Piven pulled out of his starring role in David Mamet's Broadway play "Speed-the-Plow," Dr. Carlon Colker, the primary internist treating the "Entourage" actor, detailed his debilitating condition.

"This is a situation of mercury toxicity," Colker, the medical director of Peak Wellness of Greenwich, Conn. (and a champion competitive bodybuilder) told ABCNews.com. "His level [of mercury] was quite high, almost six times the normal limit. ... In this case, it's either because of fish -- he ate sushi twice a day for years -- or because of the Chinese herbs he was taking, or both. We're pretty sure about the fish, how much the Chinese herbs contributed, we don't know. We don't have the specifics of which herbs he took."

"Right now he's being treated with bed rest; out of bed is tolerated," Colker continued. "He spent three days in the hospital, he's been discharged. He was seen by a Yale cardiologist and a professor emeritus of neurology. He's on some dietary supplements as well to protect his organ system function and to clear the mercury from the body. He also cannot eat fish."

"He'll be OK. I think it'll take a few weeks to a couple of months," Colker concluded. "Unfortunately it was like pulling teeth to get him out of the show. This is a situation that I think will resolve as long as he's attending to his health."

Piven's abrupt departure from "Speed-the-Plow" was a move deserving of its own "Entourage" episode.

"We have been advised by Jeremy Piven's medical representatives that he is seriously ill and is unable to fulfill his contractual obligation to 'Speed-the-Plow.' Consequently, he has left the production ten weeks early," the show's producers said in a statement to ABCNews.com.

In an interview Wednesday with Daily Variety, Mamet took an irreverent tone.

"I talked to Jeremy on the phone, and he told me that he discovered that he had a very high level of mercury," the playwright told Daily Variety. "So my understanding is that he is leaving show business to pursue a career as a thermometer."

Mercury Poisoning

According to the EPA, the most common way people ingest mercury is by eating fish containing methylmercury (most often tuna or swordfish) or by breaking products containing elemental mercury (like, as Mamet suggested, a thermometer).

Mercury is one of the most dangerous toxins on earth. The amount of damage it can do to a person depends on when the person is exposed (as a fetus, child or adult), the type of exposure (whether it's swallowed, touched or inhaled) and the length of the exposure.

At its worst, inhaled mercury can cause brain damage or death. Swallowing mercury can cause permanent kidney damage or death. However, according to the University of Maryland Medical Center, most exposure to mercury builds up over periods of years. In that case, mercury poisoning can cause numbness, tremors, blindness and memory problems.

Mercury poisoning treatment can last for months and usually consists of extended use of "chealator" drugs, according to the University of Maryland Medical Center.

Piven's 'Speed-the-Plow' Part to Be Picked Up By Macy, Butz

Tony Award-winner Norbert Leo Butz and Academy Award nominee William H. Macy will take on Piven's part, that of a Hollywood studio exec almost as manic as superagent Ari Gold, the character Piven plays on HBO's "Entourage." Butz starts in the play Dec. 23; Macy picks up the role Jan. 13.

In September, Piven picked up his third consecutive Emmy for his work on "Entourage" and, in his acceptance speech, alluded to the fact that small-screen acting talent doesn't necessarily translate to the stage, perhaps foreshadowing his abrupt departure from "Speed-the-Plow."

"I just got off a plane from New York in which I'm doing a play," Piven said. "And what's so interesting is that I'm in the midst of this rehearsal and I'm feeling like maybe I should go into roofing, I'm so bad. That's what it feels like right now."